With continual improvements made to microscopes over time, magnification technology advanced enough to discover cells in the 17th century. This discovery is largely attributed to Robert Hooke, and began the scientific study of cells. Over a century later, many debates about cells began amongst scientists. Most of these debates involved the nature of cellular regeneration, and the idea of cells as a fundamental unit of life. The cell theory was eventually formulated in 1839.

The three tenets to the cell theory are:
1. All living organisms are composed of one or more cells.
2. The cell is the basic unit of structure and organization in organisms.
3. Cells arise from pre-existing cells.

Which of these contributed to formation of the cell theory? Choose ALL that apply.

A. Robert Hooke observed cork cells under the microscope coining the term "cell."

B. Matthias Schleiden suggested that every structural part of a plant was made up of cells or the result of cells.
C. Theodor Schwann stated that along with plants, animals are composed of cells or the product of cells in their structures.
D. Leeuwenhoek observed motile organisms which included protozoans and other unicellular organisms, like bacteria, calling them “animalcules,” .
E. Spontaneous generation was a widely held belief that stated that some vital force contained in or given to organic matter can create living organisms from inanimate objects.